1. Field of the Invention
The present invention relates to a screw shaft feed mechanism and a positioning control method for the screw shaft feed mechanism used for a machine tool, and more specifically to a method of controlling the positioning accuracy of a screw shaft feed mechanism for moving a shaft fed base attached to a work table, for instance at a high speed and at high accuracy.
2. Description of the Related Art
A screw shaft feed mechanism for feeding a shaft fed base of a work table used for a machine tool is disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 5-215195. This mechanism is composed of a feeding screw shaft rotatably attached to a fixed member and extending in a shaft feed direction of a shaft fed base; a nut member rotatably attached to the shaft fed base and engaged with the feeding screw shaft; shaft driving means such as a motor for rotating the feeding screw shaft; and a nut driving means such as a motor mounted on the shaft fed base for rotating the nut member, so that the shaft bed base can be fed at a high speed by activating the screw shaft driving means and the nut driving means simultaneously.
In the above-mentioned screw shaft feed mechanism, however, since the screw shaft driving means and the nut driving means are activated simultaneously, although the feed speed of the shaft bed base can be increased due to the simultaneous activation of both the driving means, there exists a problem in that the positioning accuracy obtained when the shaft fed base is stopped is degraded and therefore not sufficiently high.
In particular, when the shaft fed base is a work table for a turret punch press, for instance and further if the work table cannot be located at a high accuracy, the precision of the products processed by the turret punch press is deteriorated.